(a) Field of the Invention
The present invention relates to technology of driving a panel such as a plasma display panel (PDP), and more particularly, to a PDP including first bus electrodes and second bus electrodes.
(b) Description of the Related Art
A plasma display panel (PDP) is a device for displaying characters or graphics using light emitted from plasma that is induced during gas discharge. There are direct current (DC) type and an alternating current (AC) type PDPs. They are categorized depending on what kind of applied voltage they use. Depending on the electrode structure of discharge cells, AC type PDPs can be categorized as facing surface discharging type, surface discharging type, or barrier wall discharging type. In a surface discharging type PDP, electrodes for inducing a discharge are disposed on one substrate and a fluorescent substance is disposed on another substrate, thereby reducing deterioration of the fluorescent substance due to ion bombardment during discharge. For this reason, surface discharging type PDPs have been widely used in recent years.
A typical structure of a PDP, for example, an AC surface discharging type PDP, will be described. A PDP includes a front substrate and a rear substrate. A plurality of scan electrodes and a plurality of common electrodes can be disposed on the front substrate, and bus electrodes can be respectively disposed on a surface of the scan electrodes and common electrodes. A front dielectric layer can be formed to cover the electrodes disposed on the front substrate, and a protective layer can be formed using, for example, MgO to cover the front dielectric layer. A plurality of address electrodes can be disposed on the rear substrate, and a rear dielectric layer can be formed on the rear substrate to cover the address electrodes. A plurality of barrier walls can be placed on the rear dielectric layer, and red, green, and blue phosphors can be coated between the barrier walls.
This AC surface discharging type PDP can be driven using charges formed on the dielectric layers covering the electrodes, i.e., wall charges. Address discharge can be induced in discharge spaces between the scan electrodes or the common electrodes (which are disposed in parallel on the front substrate) and the address electrodes (which face the scan electrodes and common electrodes), thereby forming surface discharge.
The bus electrodes are typically formed of Ag paste. However, the bus electrodes formed of Ag paste may detract from the luminance of the PDP by absorbing visible rays emitted from a phosphor layer formed on a rear panel and also increase luminance of reflected light. To solve these problems, the bus electrodes are sometimes replaced by double bus electrodes including, for example, black bus electrodes and white bus electrodes. An example of the double bus electrodes is disclosed in Korean Patent Laid-open Publication No. 2003-0023404. In this disclosure, some bus electrodes, which contact scan electrodes and common electrodes, are formed of black bus electrodes, and the other bus electrodes facing phosphor layers are formed of white bus electrodes. The black bus electrodes are formed of, for example, Au paste including a large amount of black pigment, so that they cannot only function as conductive bus electrodes but also effectively absorb light to reduce luminance of reflected light without using black stripes. Also, the white bus electrodes reflect visible rays emitted during gas discharge such that the black bus electrodes do not absorb them, thereby improving luminance of the PDP.
However, this PDP having the foregoing double bus electrodes involves structural problems. To be specific, since the black bus electrodes directly contact the scan electrodes and common electrodes, contact resistance between the scan/common electrodes and the black bus electrodes becomes high, thus resulting in a luminance step difference. The luminance step difference refers to a luminance difference between a region where white discharge and sustain discharge occur and a region where white discharge occurs but sustain discharge does not occur (e.g., a region adjacent to a dark portion). This luminance step difference is one of the factors affecting the quality of a screen: peak luminance, white uniformity, and contrast ratio, for example. As the luminance step difference between regions increases, it is easier for a user to recognize a difference in screen quality.
Experiments 1 and 2 show that a luminance step difference results from black bus electrodes. Experiment 1 shows case 1-1 where the bus electrodes included black bus electrodes and white bus electrodes and case 1-2 where bus electrodes included only white bus electrodes. In both cases 1-1 and 1-2, resistances and luminance step differences were measured and compared. Experiment 2 shows cases 2-1 and 2-2 where bus electrodes included black bus electrodes and white electrodes. However, while case 2-1 used white bus electrodes having high resistance, case 2-2 used white bus electrodes having low resistance. Similarly, in both cases 2-1 and 2-2, resistances and luminance step differences were measured and compared.
Experiment 1Case 1-1Case 1-2Resistance8963Luminance step difference(Max)63(cd/m2)
Experiment 2Case 2-1Case 2-2Resistance9364Luminance step difference(Max)2120(cd/m2)
As shown in the above Tables, in Experiment 1 the maximum luminance step difference in case 1-1 was twice the maximum luminance step difference in case 1-2. However, in Experiment 2, maximum luminance step differences in both cases 2-1 and 2-2 were similar. Therefore, it is clear that the poor conductive characteristic of the black bus electrodes in contact with the scan and common electrodes causes a luminance step difference, thereby deteriorating the quality of the screen.